Digital data are recorded on CDs, DVDs, and other optical media by using a laser to create pits in the surface of the medium. The data can then be read by a laser moving across them and detecting variations in the reflectivity of the surface. While this method is effective for creating machine-readable features on the optical medium, those features are not legible to the human eye.
Materials that produce color change upon stimulation with energy such as light or heat may have possible applications in imaging. For example, such materials may be found in thermal printing papers and instant imaging films. Some thermochromic coatings comprise mixtures of two or more components. The components mix and react upon application of energy, resulting in a color change. To achieve the necessary mixing, the components must react in a liquid phase. Because the coating is provided as a solid, relatively large amounts of energy are required in order to achieve the requisite melting. For example, a relatively powerful carbon dioxide laser with an energy density of 3 J/cm2 applied for longer than 100 μs may be needed to produce a mark in some films.
If the energy is being provided in the form of light, the requisite energy must not only be present, but it must be effectively absorbed and transformed into thermal energy. Depending on the application, it may be difficult to achieve the necessary level of energy absorption. Therefore, there is a need for laser-activated marking coatings that absorb light energy efficiently and are robust and easily assembled.